Ignition adapter circuit

ABSTRACT

An electrical ignition system for adapting a conventional magneto spark ignition system of a single-cylinder engine to a capacitor discharge ignition system.

Umted States Patent 1 {111 3,874,354 Crouch Apr. 1, 1975 1 IGNITIONADAPTER CIRCUIT 3.134.333 121372 Crouch 123/148 E 3,7 4.7 l l 72Wcsemeyc 123/148 E [751 Invent: Cmch, Lemme" 3.704.101 12/l972 Strubcr123/148 E [73] Assignee: Syncro Corporation, Oxford, Mich. [22] Filed:Dec. 14, 1972 Primary Examiner-Charles J. Myhre AssistantExaminer-Ronald B. Cox

Appl- 315,139 Attorney, Agent, or Firm-Harness, Dickey & Pierce [52]U.S. Cl. 123/148 E, 123/148 OC, 123/148 MC [51] Int. Cl. F02p 1/00ABSTRACT [58] new of g' 'gfi' 3 6; An electrical ignition system foradapting a conventional magneto spark ignition system of a single- [56]References Cited cylinder engine to a capacitor discharge ignition sys-UNITED STATES PATENTS 3.484.677 12/1969 Piteo .v 123/148 E 9 Claims, 2Drawing Figures IGNITION ADAPTER CIRCUIT BACKGROUND SUMMARY OF THEINVENTION The present invention relates to an adapter circuit foradapting the conventional magneto spark ignition system of asingle-cylinder engine to a capacitor discharge ignition system.

The well known advantages of a capacitor discharge ignition (CDI) systemoften render the conversion of an existing conventional magneto sparkignition system to a CDI system desirable. In a prior U.S. Pat.application, Ser. No. 207,261, filed Dec. 13, l97l, now U.S. Pat. No.3.704.397 and assigned to the same assignee as the present application.there is disclosed an ignition adapter circuit for converting aconventional magneto spark ignition system of a two-cylinder, two-cycleengine to a CDI system. In that type of engine, a pair of breaker pointsare individually associated one each with each of the cylinders. and theproper operation of the adapter circuit requires the use of both sets ofbreaker points.

In contrast to a two-cylinder, two-cycle engine, a single-cylinderengine having a conventional magneto spark ignition system utilizes onlya single set of breaker points. The present invention provides anadapter circuit which is suitable for use with a singlecylinder engineand which obtains a desired objective of eliminating any need formechanical revision or modification of the existing ignition hardwarewhen installing the adapter circuit. In other words, the adapter circuitof this invention is installable by simply mounting the adapter on theengine and remaking at most a few simple electrical connections.

Important features. advantages and benefits of the invention will beseen in the ensuing description and claims which are to be taken inconjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a preferredembodiment of the invention in accordance with the best mode presentlycontemplated for carrying out the invention.

FIG. 1 is an electrical schematic diagram of an ignition adapter circuitaccording to the present invention coupled with a pre-existing magnetospark ignition system of a single-cylinder engine to render it a CDIsystern.

FIG. 2 is an electrical schematic diagram of another ignition adaptercircuit according to the present invention coupled with a pre-existingmagneto spark ignition system of a single-cylinder engine to render it aCDI system.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, an ignition adaptercircuit according to the present invention is coupled with a magnetoignition section 12 and an ignition coil and plug section 14. In thepre-existing conventional system for a singlecylinder engine. section 12is directly coupled with section I4.

Section 12 comprises a magneto coil 16, a capacitor 18, and a set ofbreaker points 20. Magneto 16 is mounted on the engine typically infixed position on a stator (not shown). The stator is in proximity to aflywheel (not shown) which rotates with the engine. Magneto I6 isenergized by one or more sets of magnetic pole pairs (not shown) whichrotate with the flywheel. In this way as the flywheel turns, analternating magnetic flux is developed in magneto 16 which causesmagneto 16 to supply an alternating polarity output to its load. Magnetol6, capacitor 18, and points 20 are connected in parallel with eachother across an output terminal and ground G. Breaker points 20 aremounted on the engine for actuation in timed relation with the rotationof the engine to achieve proper timed engine firing. Capacitor I8 isconventionally provided to minimize arcing across points 20.

Section I4 comprises an ignition coil 22 and a spark plug 24. Coil 22comprises a primary winding 26 and a secondary winding 28 which areconnected to a common grounded terminal 14b. Spark plug 24 is connecteddirectly across secondary winding 28. In the pre-existing conventionalignition system, primary winding 26 is connected in parallel with points20, capacitor 18, and magneto 16 via an input terminal and ground G,terminal 140 being directly connected to terminal 12a. In theconventional system, the opening of points 20 causes the output ofmagneto coil 16 to be supplied to primary winding 26, the opening ofpoints 20 occurring when the output of magneto coil I6 is of positivepolarity. The electrical energy delivered to primary winding 26 in turncauses a rapid change in the magnetic flux linking windings 26 and 28and hence a voltage to be developed across secondary winding 28 forfiring spark plug 24. Thus, plug 24 fires in timed relation with theopening of points 20 to produce desired fuel ignition within the enginecylinder.

In order to convert the pre-existing conventional ignition to CDI. theconnection between terminal 120 and terminal 14a is broken and adaptercircuit 10 is connected therebetween. An input terminal 100 of adapter10 is connected to terminal 120, an output terminal 10b to terminal 14a,and a third terminal 10c to ground G. Adapter circuit 10 comprises acapacitor 30 and a diode 32 connected in series between terminals 10aand 10c. Plate 300 of capacitor 30 is connected to terminal 100, plate30b of capacitor 30 to the anode terminal 320 of diode 32, and thecathode terminal 32b of diode 32 to terminal 100. Circuit 10 furthercomprises an SCR 34 having an anode terminal 34a connected to terminal10b, a cathode terminal 34b connected to the junction of capacitor 30and diode 32, and a gate terminal 34c connected through the seriescombination ofa resistor 36 and a diode 38 to terminal 10a. One terminalof resistor 36 is connected to terminal 34c, the other terminal ofresistor 36 to the cathode terminal 38a of diode 30a, and the anodeterminal 38b of diode 38 to terminal 100. A diode 40 has its anodeterminal 40a connected to the junction of capacitor 30. diode 32 and SCR34 and its cathode terminal 40b to the junction of SCR 34 and primarywinding 26. Adapter circuit 10 is desirably packaged as a compact unithaving terminals 10a, 10b and IOCavailable for connection. It will beobserved that in order to install adapter circuit 10 on the engine, allthat is required is breaking the connection between terminals I2a and14a, and making the connections to terminals 10a, 10b and 10c. Thus theinstallation is simple and straightforward, requiring no mechanicalmodification or revision to pre-existing ignition hardware.

With adapter circuit 10 installed, the CDI system operates as follows.For the illustrated embodiment of FIG. I, it will be remembered thatpoints 20 open when the output waveform of magneto coil 16 is positive.The timing of points 20 is such that the points remain open during aninitial portion of the immediately succeeding negative polarity portionof the magneto output waveform. Accordingly, during this initial portionof the negative polarity portion, current flows from coil 16 via diode32 to charge capacitor 30 such that plate 30b becomes negative withrespect to plate 30a. Thus, voltage of the illustrated polarity isdeveloped across capacitor 30 before the next positive polarity portionof the magneto output waveform during which points 20 will again open.It will be observed that capacitor 30 also forms a series circuit withprimary winding 26 and SCR 34. SCR 34 is arranged to permit capacitor 30to discharge into primary winding 26. However, to render SCR 34conductive, it is necessary that a suitable gating signal be applied toterminal 34c. So long as points 20 remain closed, magneto 16 supplies noinput to adapter circuit 10, and hence cannot provide the necessarygating signal to render SCR 34 conductive. However, when points 20 open(which is when the output of magneto 16 is positive) the magneto outputis applied to terminal 100, and in turn to SCR terminal 34c via diode 38and resistor 36. This is sufficient to develop the necessary gatingsignal at terminal 34c for rendering SCR 34 conductive. Thus with SCR 34becoming conductive in response to the opening of points 20, capacitor30 immediately discharges into primary winding 26. This in turn causes arapid change in the magnetic flux linking windings 26 and 28 and hence avoltage to be developed across secondary winding 28 for firing sparkplug 24. Since the discharge of capacitor 30 into pri* mary winding 26tends to be oscillatory, diode 40 permits conduction of current in theopposite direction from that of the current flow through SCR 34. Whencurrent flows through diode 40, a reverse voltage is developed acrossSCR 34 and this reverse voltage is advantageously used to positivelyturn off SCR 34 and thereby prevent energization of primary winding 26by magneto coil 16 when capacitor 30 is being charged. In this way, theinvention provides a CDI system in which the firing of the spark plug isinitiated by the opening of points 20 as was the case for thepre-existing conventional ignition system. Thus, the invention achievesthe desired objective of being capable of installation in a pre-existingsingle-cylinder engine without modifica tion or revision of preexistingignition hardware.

FIG. 2 illustrates another form of the invention which is useful insinglecylinder engines wherein the breaker points open when the polarityof the magneto output is negative. In FIG. 2 like numerals are used toindicate iike components, and the only differences between the circuitsof FIGS. 1 and 2 are as follows. Since breaker points 20 open during thenegative polarity output of magneto l6, diodes 32 and 38 are connectedin opposite fashion from their connection in FIG. 1. SCR 34 is replacedby a triac 42 which comprises terminals 42a, 42b and 42c. Diode 40 isnot required.

The circuit of FIG. 2 operates with respect to negative polarity magnetooutput in the same way that the circuit of FIG. 1 operates with respectto positive polarity magneto output. In other words. during an initialportion of the positive portion of the magneto output waveform,capacitor 30 is charged via diode 32 to make plate 30b positive withrespect to plate 300. Dur ing the immediately succeeding negativeportion of the magneto output, breaker points 20 open to provide agating signal to triac 42 and this renders triac 42 conductive.Capacitor 30 discharges into primary winding 26 causing spark plug 24 tofire. Since triac 42, once triggered, can conduct current flow in bothdirections, diode 40 is not required. Triac 42 later becomesnonconductive to prevent energization of primary winding 26 by magneto16 when capacitor 30 is being charged and triac 42 remainsnon-conductive until again triggered by points 20 opening. Thus in thecircuit of FIG. 2, the firing of plug 24 is initiated by the opening ofpoints 20 as in the conventional system. Accordingly, the adaptercircuit of FIG. 2 also can be used without modification or revision ofpre-existing ignition hardware.

While it will be apparent that the preferred embodiments of theinvention disclosed are well calculated to fuifill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the spiritthereof.

I claim:

1. For a single-cylinder engine having an existing magneto sparkignition system which comprises a magneto coil for supplying alternatingpolarity output waveform, an ignition coil having primary and secondarywindings. a spark plug operatively coupled with the secondary windingand means operatively coupling the magneto coil with the primary windingcomprising a single set of breaker points actuatable between open andclosed conditions in timed relation with operation of the engine forcausing the spark plug to fire, an adapter assembly for converting theexisting magneto spark ignition system to a capacitor discharge ignitionsystem and interconnectable between the set of breaker points and theprimary winding of the ignition coil, said adapter assembly comprising acapacitor, input circuit means for operatively coupling said capacitorwith the points and the magneto, said input circuit means comprisingmeans for causing said capacitor to be charged by at least a portion ofone polarity of the alternating output waveform of the magneto when theset of breaker points is in one condition and output circuit means foroperatively coupling said capacitor with the primary winding, saidoutput circuit means comprising means responsive to the actuation of theset of breaker points to the other condition for causing said capacitorto discharge through the primary winding and thereby cause the sparkplug to tire.

2. The adapter assembly of claim I wherein said input circuit meanscomprises a diode operatively coupling the points and the magneto withsaid capacitor, said diode being arranged to conduct charging current tosaid capacitor from the magneto.

3. The adapter assembly of claim 1 wherein said output circuit meanscomprises a solid state switch operatively coupling said capacitor withthe primary winding and means operatively coupling said solid stateswitch with the breaker points for initiating conduction of said solidstate switch when the set of breaker points is actuated to the othercondition and causing said capacitor to discharge through the primarywinding and fire the spark plug.

4. the adapter assembly of claim 3 wherein said solid state switch is anSCR.

5. The adapter assembly of claim 3 wherein said solid state switch is atriac.

6. The adapter assembly of claim 1 wherein said means responsive to theactuation of the set of breaker points to the other condition comprisesmeans responsive to the opening of the set of breaker points for causingsaid capacitor to discharge through the primary winding.

7. For a single-cylinder engine having an existing magneto sparkignition system which comprises a magneto coil for supplying alternatingpolarity output waveform relative to a ground potential, an ignitioncoil having primary and secondary windings a spark plug operativelycoupled with the secondary winding and means operatively coupling themagneto coil with the primary winding comprising a single set of breakerpoints actuatable between open and closed conditions in timed relationwith operation of the engine for caus ing the spark plug to fire. anadapter assembly for converting the existing magneto spark ignitionsystem to a capacitor discharge ignition system and interconnectablebetween the set of breaker points and the primary winding of theignition coil, said adapter assembly comprising a capacitor, inputcircuit means for operatively coupling said capacitor with the set ofbreaker points and the magneto, said input circuit means comprisingmeans for causing said capacitor to be charged by at least a portion ofone polarity of the alternating output of the magneto such that oneterminal of said capacitor is charged to a potential of said onepolarity relative to ground potential when the set of breaker points isin one condition and output circuit means for operatively coupling saidcapacitor with the primary winding. said output circuit means comprisinga thyristor having an anode and a cathode defining a principalconduction path through the thyristor and a gate for establishingconduction through the principal conduction path between said anode andsaid cathode, means connecting said cathode with said one terminal ofsaid capacitor, and means connecting said gate with the set of breakerpoints when the set of breaker points is actuated to the other conditionso that said thyristor is triggered into conduction by the differencebetween the respective potentials applied to said cathode and said gatewhereby said capacitor discharges through said thyristor and into theprimary winding and thereby causes the spark plug to tire.

8. The adapter assembly of claim 7 wherein said thyristor is an SCRv 9.The adapter assembly of claim 77 wherein said thyristor is a triac.

1. For a single-cylinder engine having an existing magneto spark ignition system which comprises a magneto coil for supplying alternating polarity output waveform, an ignition coil having primary and secondary windings, a spark plug operatively coupled with the secondary winding and means operatively coupling the magneto coil with the primary winding comprising a single set of breaker points actuatable between open and closed conditions in timed relation with operation of the engine for causing the spark plug to fire, an adapter assembly for converting the existing magneto spark ignition system to a capacitor discharge ignition system and interconnectable between the set of breaker points and the primary winding of the ignition coil, said adapter assembly comprising a capacitor, input circuit means for operatively coupling said capacitor with the points and the magneto, said input circuit means comprising means for causing said capacitor to be charged by at least a portion of one polarity of the alternating output waveform of the magneto when the set of breaker points is in one condition and output circuit means for operatively coupling said capacitor with the primary winding, said output circuit means comprising means responsive to the actuation of the set of breaker points to the other condition for causing said capacitor to discharge through the primary winding and thereby cause the spark plug to fire.
 2. The adapter assembly of claim 1 wherein said input circuit means comprises a diode operatively coupling the points and the magneto with said capacitor, said diode being arranged to conduct charging current to said capacitor from the magneto.
 3. The adapter assembly of claim 1 wherein said output circuit means comprises a solid state switch operatively coupling said capacitor with the primary winding and means operatively coupling said solid state switch with the breaker points for initiating conduction of said solid state switch when the set of breaker points is actuated to the other condition and causing said capacitor to discharge through the primary winding and fire the spark plug.
 4. the adapter assembly of claim 3 wherein said solid state switch is an SCR.
 5. The adapter assembly of claim 3 wherein said solid state switch is a triac.
 6. The adapter assembly of claim 1 wherein said means responsive to the actuation of the set of breaker points to the other condition comprises means responsive to the opening of the set of breaker points for causing said capacitor to discharge through the primary winding.
 7. For a single-cylinder engine having an existing magneto spark ignition system which comprises a magneto coil for supplying alternating polarity output waveform relative to a ground potential, an ignition coil having primary and secondary windings, a spark plug operatively coupled with the secondary winding and means operatively coupling the magneto coil with the primary winding comprising a single set of breaker points actuatable between open and closed conditions in timed relation with operation of the engine for causing the spark plug to fire, an adapter assembly for converting the existing magneto spark ignition system to a capacitor discharge ignition system and interconnectable between the set of breaker points and the primary winding of the ignition coil, said adapter assembly comprising a capacitor, input circuit means for operatively coupling said capacitor with the set of breaker points and the magneto, said input circuit means comprising means for causing said capacitor to be charged by at least a portion of one polarity of the alternating output of the magneto such that one terminal of said capacitor is charged to a potentiAl of said one polarity relative to ground potential when the set of breaker points is in one condition and output circuit means for operatively coupling said capacitor with the primary winding, said output circuit means comprising a thyristor having an anode and a cathode defining a principal conduction path through the thyristor and a gate for establishing conduction through the principal conduction path between said anode and said cathode, means connecting said cathode with said one terminal of said capacitor, and means connecting said gate with the set of breaker points when the set of breaker points is actuated to the other condition so that said thyristor is triggered into conduction by the difference between the respective potentials applied to said cathode and said gate whereby said capacitor discharges through said thyristor and into the primary winding and thereby causes the spark plug to fire.
 8. The adapter assembly of claim 7 wherein said thyristor is an SCR.
 9. The adapter assembly of claim 77 wherein said thyristor is a triac. 